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(EXP1/09) Internal Transport Barrier and $\beta$ Limit in Ohmically Heated Plasma in TUMAN-3M

M. V. Andreiko, L. G. Askinazi, V. E. Golant, N. A. Zhubr, V. A. Kornev, S. V. Krikunov, S. V. Lebedev, L. S. Levin, G. T. Razdobarin, V. V. Rozhdestvensky, V. A. Rozhansky¹ , A. I. Smirnov, M. Tendler² , A. S. Tukachinsky, S. P. Yaroshevich

Ioffe Physico-Technical Institute, Russian Academy of Sciences, St.Petersburg, RUSSIA
¹ St.Petersburg State Technical University, St.Petersburg, RUSSIA
² Alfven Lab., EURATOM-NFR Assoc., Royal Institute of Technology, Stockholm, SWEDEN

Abstract.  An Internal Transport Barrier (ITB) was found in ohmically heated plasma in TUMAN-3M (R₀ = 53 cm, a_l = 22 cm - circular limiter configuration, B_t $\leq$ 0.7T, I_p $\leq$ 175 kA, < n > $\leq$ 6.0 ^. 10¹⁹m^-3). The barrier reveals itself as a formation of a steep gradient on electron temperature and density radial profiles. The regions with reduced diffusion and electron thermal diffusivity are in between r = 0.5a and r = 0.7a. The ITB appears more frequently in the shots with higher plasma current. At lower currents (I_p < 120 kA) the ITB is rare. In the ohmic H-mode with ITB the thermal energy confinement is in the range of 9-18 ms. The enhancement factor over ITER93-H(ELM-free) scaling is up to 2. The results of experimental study of $\beta_{N}^{}$ limit in the ohmically heated plasma are presented. Stored energy was measured using diamagnetic loops and compared with W calculated from kinetic data obtained by Thomson scattering and microwave interferometry. Measurements of the stored energy and of the $\beta$ were performed in the ohmic H-mode before and after boronization and in the scenario with the fast Current Ramp-Down in the ohmic H-mode. Maximum value of $\beta_{T}^{}$ of 2.0 % and $\beta_{N}^{}$ of 2 were achieved. The $\beta_{N}^{}$ limit achieved is ``soft'' (nondisruptive) limit. The stored energy slowly decays after the Current Ramp-Down. No correlation was found between beta restriction and MHD phenomena.

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